The present invention relates to an image forming apparatus used in a copying machine, printer, facsimile machine, and combinations of these machines. Specifically, an image forming apparatus is provided which uses an exposing device composed of light emitting diodes arranged in the axial direction of a photo conductor and a lens array provided in correspondence to said light emitting diodes and performs gradational representation of each of the dots composing the image by varying the amount of light emission of said light emitting diodes. The granularity (graininess) of the printed image is improved and the roughness and irregularity in density in the printed image, or rough image, is prevented.